As a NAND flash memory, a three-dimensionally stacked memory formed by batch processing and stacking layers in the vertical direction has been proposed in order to suppress the increase in process cost.
In this three-dimensionally stacked memory, a cylindrical hole (memory hole) is formed at once through a plurality of electrodes stacked on a semiconductor substrate, and a memory film is formed on the inner wall of the hole. After that, polysilicon (a silicon pillar) functioning as a channel is formed inside the hole. This makes it possible to form a NAND string (memory string) including a plurality of MONOS memory cells connected in series in the stacking direction at once.
Furthermore, as the three-dimensionally stacked memory described above, a memory in which a U-shaped silicon pillar including a pair of pillar portions and a connecting portion connecting the lower ends of the pillar portions is used as a channel has been proposed. In this memory, a memory string is formed along the U-shaped silicon pillar.